Equipment Integration – Turbines can be pre-coupled to a crude distillation unit (or other continuously operated processes with an applicable temperature range). The off gases of the gas turbine can be used to supply the heat for the distillation furnace, if the outlet temperature of the turbine is high enough. One option is the so-called `repowering’ option.
Equipment Integration in Plants & Refineries | Energy Conservation
In this option, the furnace is not modified, but the combustion air fans in the furnace are replaced by a gas turbine. The exhaust gases still contain a considerable amount of oxygen, and can thus be used as combustion air for the furnaces. The gas turbine can deliver up to 20% of the furnace heat. Two of these installations are already installed in some industrial facilities, with a total capacity of 35 MWe. A refinery in US has installed a 16 MWe gas turbine at a reformer. The flue gases of the turbine feed to the convection section of the reformer increasing steam generation. The steam is used to power a 20 MWe steam turbine.
Another option, with a larger combined heat and power potential and associated energy savings, is “high-temperature combined heat and power”. In this case, the flue gases of a combined heat and power plant are used to heat the input of a furnace or to preheat the combustion air. This option requires replacing the existing furnaces. This is due to the fact that the radiation heat transfer from gas turbine exhaust gases is much smaller than from combustion gases, due to their lower temperature.
A distinction is made between two different types. In the first type, the exhaust heat of a gas turbine is led to a waste heat recovery furnace, in which the process feed is heated. In the second type, the exhaust heat is led to a “waste heat oil heater” in which thermal oil is heated. By means of a heat exchanger, the heat content is transferred to the process feed. In both systems, the remaining heat in the exhaust gases after heating the process feed should be used for lower temperature purposes to achieve a high overall efficiency.
One option is to use this low grade energy to produce cooling capability in absorption chillers for instance and use such cooling capability to save power in other applications in the process or in producing more power from CGT via its inlet air cooling. The second type is more reliable, due to the fact that a thermal oil buffer or other media can be included. The main difference is that in the first type the process feed is directly heated by exhaust gases, where the second uses thermal oil or other media as intermediate, leading to larger flexibility and/or may be more economical impact.
It is a little difficult to end this chapter with a list of references since this chapter is merely a collection of experiences and versatile knowledge gained from the field work and from many of the smart plants operators worldwide along several years. Hence, instead of a list of references, I will rather close it with a useful check list of energy conservation items.